The scores are relative to each system, as each piece of hardware has its own technical standards and expectations.
NBA 2K14 on the Xbox 360 has pretty much maxed out the system's technical capabilities. It's about as good as a basketball game is going to be on eight-year-old hardware, hence the higher overall score. Like Larry Brown taking the Charlotte Bobcats to the playoffs, it's doing great things with not a lot of raw physical talent.
NBA 2K14 on the PlayStation 4 is presumably just scratching the surface of what's possible on the system. It might be a better game than the Xbox 360 version when you put the two side by side, but the PS4 version still scores lower overall because it doesn't seem to be getting as much out of the powerful PlayStation 4 hardware as the Xbox 360 version is getting out of much weaker technology. That would make the PS4 edition the "Scott Brooks" version of NBA 2K14: it still performs at a high level, but you can't help but feel like it could be doing a lot better than it is with so much power at its disposal.